This invention relates to an engine controller equipped with knocking detection means and more particularly to an engine controller which is controlled by judging occurrence of knocking using a knocking judgement index based on a vibration power spectra of resonance frequencies.
When knocking occurs in a engine, a vibration having specific resonance frequency components occurs. Detection of occurrence of knocking is attained by separating vibration resulting from the occurrence of knocking from background vibration, in the vibration which constitutes the overall engine vibration detected by a vibration sensor.
As described in Japanese Patent Laid-open No. 58-45520 (1983) a conventional knocking detector preliminarily selects and separates a single resonance frequency component within the range of 5 to 10 KHz from the engine vibration by use of a bandpass filter and judges the occurrence of knocking by judging whether or not this resonance frequency component is greater than a predetermined level.
Since the prior art technique described above judges the existence of occurrence of knocking by use of only the single frequency component contained in the output of the vibration sensor, the deviation of background vibration becomes greater than the vibration due to the occurrence of knocking at the time of a high load, high speed operation where the background vibration becomes great. Accordingly, the vibration due to the occurrence of knocking and the background vibration cannot be effectively separated from the output of the vibration sensor, and so the detection of the occurrence of knocking cannot be made.